$.$ We have studied a waiting time model for systems which are subject to variability $($demand or process$)$ variability. Below is the utilization curve for systems with $1$ server $($m $=1)$ and multiple servers $($m $=2,$ m $=5,$ m $=10).$Describe how the Waiting Time, Tq$,$ changes for utilization of $90\%$ for m $=1$ to m $=5.$

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Select one only:

a$.$ System variability leads to an increase in flow time because inventory builds up in the system and causes queuing.

b$.$ System variability causes inventory to be reduced in the process.

c$.$ System variability allows bottleneck utilization to be greater than $100$ percent.

d$.$ System variability means that customers will never have to wait.